Piezoelectric generators for ammunition



.,1. VILBAJO 393499709 PIEZOELECTRIC GENERATORS FOR MMUNITION Oct. 3l, 1967 Filed Sept. 22 1964 INVENTOIZ @Lkwchdzr ATTQrLNEas United States Patent O 3,349,709 PIEZOELECTRIC GENERATORS FOR AMMUNTION .lean Vilbajo, Brussels, Belgium, assignor to Contigea Societe Anonyme, Brussels, Belgium Filed Sept. 22, 1964, Ser. No. 398,303 Claims priority, application Belgium, Sept. 30, 1963,

637,974; Aug. 31, 1964, 652,466 3 Claims. (Cl. 102-70.2)

The more and more common use in electric fuses of ferro-electric materials and more particularly of Ibarium titanate, sets `an extremely important problem on which depends the development and the efficiency of the ammunition. Indeed, on the one hand, it is well known that the piezoelectric effect does not only require an applied effort, however important, but that it also wants the presence of a deformation for securing the production of the necessary electric current. On the other hand, when a high-speed impact occurs, there occur in the ferroelectrics, propagations of pressure waves which cause the material to be destroyed without giving rise to the compressions which are indispensable for aforesaid production of electric current. These propagations are due to aforesaid impact velocity, which places the generator into plastic or even hydrodynamic conditions.

The problem thus mainly consists in introducing into the generator, without diminishing the velocity of the actual projectile, means which are able to prevent the collapse -by shearing of the material, before the appearance into the generator of a compression effort which is considerable, respectively sufficient for generating the necessary electric current. This means will therefore, without diminishing the own velocity of the projectile, have to enable the transfer to the grenerator, at the proper moment, of the static pressure capable of producing the deformation previous to the piezoelectric effect.

Several means have already been suggested, obviously in order to partially damp the effects of the impact at the location of the generator, or at least for very slightly delaying the transmission of these effects lby inserting, between the actual generator and the tip of the shell, a damping device or an elastic element.

A first means consisted in putting over the generator an elastic cap which thus forms, so to say, the tip of the shell. It is hoped, by this means, to delay somewhat the instant of actual transmission of the impact effects onto the generator, which in this instance, is evidently quite questionable, this delay being essentially variable, depending for instance on the angles of impact, considering namely that the deformation of the elastic masses can here take place in all directions.

An alternative to this means consisted in inserting, between the generator and the ti-p of the shell, such an elastic cap acting, so to say, as an insert and designed so as to be able to undergo a continuous deformation until and including the phase when the effects of the impact are transmitted to the generator.

In fact, if in this kind of disposition, the deformations of the elastic mass can be more readily oriented than in the preceding case, and if, on the other hand, there occurs a certain braking effect in the transmission of the impact effects to the generator, it must be admitted that the amplitude of the pressure waves which are actually transmitted to the ferro-electric material remains practically unchanged, which also renders this means rather doubtful.

Finally, it has also been suggested to insert a coil spring between the generator and the tip of the shell. This device may be considered as technically equivalent to the previous one, considering that the presence of such spring, even and particularly after being compressed until its windings are contiguous, is not capable of bringing `about the required reduction of the pressure wave amplitude.

The present invention concerns improvements which, contrary to the various means which have been suggested before, fulll the essential condition which consists not only in securing a braking effect and a delay of the impact effort transmitted to the generator, but also and mainly in securing simultaneously a reduction of the pressure wave amplitude, so that this amplitude should not be altogether transmitted to the ferro-electric material.

The result of the foregoing is that these improvements make it possible to design electric fuses in such way that even very high impact velocities of the projectile can still be adopted whilst securing in the generator the deformation which is required for the piezoelectric effect, even if the pressure wave at impact is itself suihcient for causing the destruction of the ferro-electric materials without creating the required compression effects.

The improvements according to the present invention essentially consist in putting, in front of the piezoelectric device, in a totally closed housing with rigid walls, an elastic shield-pad the volume of which is slightly smaller than that of the housing itself.

This shield-pad is placed between the generator and the tip of the shell. It will generally consist of a mass of some elastic material suc-h as natural or artificial rubber, Whose form shall be slightly diierent from that of its housing in order to leave a certain spacing between them. The housing shall preferably be limited by the cooperation of a lixed part and a mobile part co-axial to it, aforesaid mobile part being able, under the effect of the impact, to move in the axial direction, being duly guided thereby by the xed part in order to compress and distort aforesaid shield-pad, the pressure waves being thus partially absorbed by the latter under duly predetermined conditions and the transmission to the generator of the pressure waves whose intensity has thus been reduced taking place under the optimum conditions required for obtaining the piezoelectric eifect.

These improvements make it possible for the specialist of these questions to control with a considerable amount of accuracy the manufacture and the design of electric fuses by an optimum determination of the rigid and entirely closed housing, of the shape of the shieldpad and of the means for securing the transmission of the damped pressure waves to the generator. For this purpose it will be possible, conforming to the present invention, to insert with considerable advantage, between aforesaid fixed part of the rigid and entirely closed housing of the screen-pad and the actual generator, simple means for correctly polarizing aforesaid transmission of the pressure waves to the generator. One of such means might consist for instance in the insertion of a ball.

Aforesaid characteristic elements may of course be applied and used in various forms and dimensions, according to the case.

Merely by way of example and without implying any restrictive conditions, one form of embodiment is described in further detail hereafter, with refernce to the appended drawings of which:

FIGURE l illustrates a radial section of an improved piezoelectric generator conforming to the present invention, in its resting or standby position;

FIGURE 2 is similar to FIGURE l, but the generator is represented in the position following an impact.

In this form of embodiment, the shield-pad 1 is placed in a housing provided between the nose 2 and the generator 3 with the help of the pistons 4-5 and of an intermediate ball 6. The housing 7 of aforesaid shield-pad 1 on the one hand, and the form and/ or the dimensions thereof on the other hand, are such that there is in aforesaid housing 7 at least one free space 8. The difference between the volumes of aforesaid housing 7 and aforesaid shield-pad is suiciently restricted for preventing the pressure waves from being transmitted, although it is not sufficiently restricted for delaying the application of the pressure to the projectile. As soon as the shield-pad 1 fills the whole volume of housing 7, it can practically not be compressed any further and, in this state, it transmits the impact stress. The shield-pad 1 shall preferably be made of rubber and the latter shall be of such quality that, on account of its comparatively low density and the velocity with which sound is transmitted through the actual rubber material, aforesaid shield-pad 1 prevents the passage of the pressure wave.

It results therefrom that, when an impact occurs, the generator is first of all subjected to an increasing effort due to the resistance to deformation of the rubber, then, to an effort corresponding to the maximum compression of rubber and, finally, to the stress of the impact through the rubber which has thus become practically incompressible.

The presence of the intermediate ball 6 acting as a ball joint between the nose 2 and the generator 3 will contribute to a better distribution of the effort over the whole extent of generator 3, even if the impact happens to be a slant.

Nothing prevents however from using any other type of construction which is able to lead to equivalent results.

Concerning more particularly the difference of volume between the shield-pad ll and its housing 7 which is entirely closed by rigid walls, this particular feature should be considered in its wider sense. This diiference of volume may either be due to a difference of dimensions, to a difference of form or also to the presence of hollow parts provided either in the shield-pad, in its housing, or in both of them.

In one very particular form of embodiment, the free spaces between the actual shield-pad and its housing might be lled by a material which is considerably more subject to deformation, respectively to compression, than the actual shield-pad. Such kind of construction might for instance be applied by using a shield-pad of at least two different materials of which one would form the actual shield-pad whilst the other would act as a filler with a much higher deformability, respectively elasticity, than the actual shield-pad. In such kind of embodiment, consideration should be given to aforesaid filling material between the shield-pad and its closed housing with rigid walls.

The present invention concerns such an improved electric fuse as well as any projectile fitted therewith.

What I claim is:

1. A projectile comprising a head, a hollow nose displaceably mounted in said head, said nose having rigid walls partly extending beyond said head and partly eX- tending into said head, a piston slidably mounted in said hollow nose between said walls, said walls and said piston enclosing a chamber, an elastic shield-pad mounted on said piston and located within said chamber, a piezoelectric element mounted in said head, and means operatively connecting said piezoelectric element with said piston.

2. A projectile in accordance with claim 1, wherein said shield-pad has portions spaced from said walls.

3. A projectile in accordance with claim 1, wherein said means comprise a ball engaging said piston, and an intermediate member engaging said ball and said piezoelectric elements.

References Cited UNITED STATES PATENTS 2,849,957 9/1958 Kuller et al. IGZ-70.2 2,892,411 6/1959 Brown et al 102-70.2 3,031,968 5/1962 Dowdell et al. 102-70.2 3,202,100 8/1965 Vilbajo IGZ-70.2

BENJAMIN A. BORCHEL'I', Primary Examiner.

SAMUEL FEINBERG, Examinez'.

W. C. ROCH, Assistant Examiner. 

1. A PROJECTILE COMPRISING A HEAD, A HOLLOW NOSE DISPLACEABLY MOUNTED IN SAID HEAD, SAID NOSE HAVING RIGID WALLS PARTLY EXTENDING BEYOND SAID HEAD AND PARTLY EXTENDING INTO SAID HEAD, A PISTON SLIDABLY MOUNTED IN SAID HOLLOW NOSE BETWEEN SAID WALLS, SAID WALLS AND SAID PISTON ENCLOSING A CHAMBER, AN ELASATIC SHIELD-PAD MOUNTED ON SAID PISTON AND LOCATED WITHIN SAID CHAMBER, A PIEZO- 